The present invention relates to a polymerizable compound, a polymer formed from this compound, a dental material containing this compound, a method for polymerizing this compound in situ on teeth, and a tooth comprising a polymer of this compound.
In recent years, the use of polymer-based dental materials became very prominent as they improved aesthetics and durability of restorations, faciliated application techniques and allowed great expansion of dental techniques in restorative, corrective and preventive applications. Especially important became filled restorative material, cements, bonding agents, fissure sealers and orthodontic adhesives based on the polymerizable in situ aromatic and aliphatic methacrylates. The best properties in these materials have been obtained when the resin part of the composition is comprised of one or more of the following monomers: ##STR3## i.e., 2,2-bis [4'(3"-methacroyl-2"-hydroxypropoxy)phenyl] propane (known in the industry as Bis-GMA), its adducts with various alkyl-isocyanate, such as adducts described in the Waller U.S. Pat. No. 3,629,187, the entire disclosure of which is hereby incorporated by reference and relied upon, and ##STR4## i.e., 2,2-bis[4'(2"-methacroylethoxy)phenyl] propane (known in the industry as EBA).
These high molecular weight monomers are usually diluted with lower molecular weight polymethacrylates including dimethacrylates such as di-, tri- or tetraethylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, or trimethacrylates such as trimethylolpropane trimethacrylate. Other methacrylate monomers known to be used in certain restorative materials, cements, fissure sealers, bonding agents or orthodontic adhesives and claimed to improve mechanical, physical, clinical or aesthetic properties of materials are: ##STR5## i.e., 2-methacroylethyl-3-methacroyl-2-hydroxypropyl tetrahydro (or hexahydro) phthalate and ##STR6## i.e., 2,2 bis(4'-methacroylphenyl)propane (known in the industry as BADM).
In an attempt to improve methacrylate resin based dental materials, research efforts have been concentrated mainly on reducing their water sorption, as related to susceptibility to hydrolysis and staining, on monimizing their polymerization shrinkage and on improving their resistance to discoloration when exposed to sunlight.
These properties depend on the chemical structure of the monomer or monomers used in the formulation and their purity. In the formulations containing (besides the resin binder) a solid phase in the form of dispersed filler particles, the viscosity of the resin constitutes another important factor. The lower the viscosity of the alternative monomers that may be used in the formulation, other properties remaining similar or the same, the more filler may be incorporated in the formulation contributing to lower shrinkage, lower water sorption, better wear resistance and overall improved mechanical properties.
As it is recognized in the dental profession, the composite restoratives known up to now were unsuitable in most instances for use in posterior restorations, mainly because of their unsatisfactory wear resistance. This is especially true for Class II restorations as exposed the most to strong mastication forces. The typical properties of composite restoratives made according to presently known techniques are given below:
Water Sorption as 37.degree. C. 0.7 mg/cm.sup.2 PA1 Compressive Strength 30,000-40,000 psi PA1 Diametral Tensile Strength 3,480-4,600 psi* PA1 Color Stability Discoloration perceptible with difficulty PA1 Hardness (Barcol) 98 PA1 Opacity/Translucency 0.35-0.55* PA1 Filler/Resin ratio by Weight 3.2:1 to 4.2:1 FNT * Determined according to American Dental Association Specification No. 27, JADA, Vol. 94, June, 1977. PA1 R.sub.1 and R.sub.2 are the same or different and are hydrogen or groups of the formula ##STR8## where R.sub.3 is an aliphatic, aromatic or cycloaliphatic group having 1 to 14 carbon atoms. PA1 R.sub.1 and R.sub.2 are the same or different and are hydrogen or groups of the formula: ##STR10## where R.sub.3 is an aliphatic, aromatic or cycloaliphatic group having 1 to 14 carbon atoms. Dimethacrylate compounds of this formula are referred to herein as compounds of the present invention.
In addition to the above-mentioned Waller U.S. Pat. No. 3,629,187, various polymeric dental materials have been described in the following U.S. Pat. Nos. 3,066,112 (Bowen); 3,179,623 (Bowen); 3,194,783 (Bowen); 3,194,784 (Bowen); 3,539,533 (Lee II et al); 3,541,068 (Taylor); 3,597,389 (Taylor); 3,721,644 (Stoffey et al); 3,730,947 (Stoffey et al); 3,751,399 (Lee, Jr. et al); 3,766,132 (Lee, Jr. et al); 3,774,305 (Stoffey et al); 3,860,556 (Taylor); 3,926,906 (Lee, II et al); 4,102,856 (Lee, Jr.); and 4,107,845 (Lee, Jr. et al) and 3,862,920 (Foster et al). Further information on polymer based dental materials is given on pages 501-508 and 515-517 of the Kirk-Othmer Encyclopedia of Chemical Technology, Third Edition, Volume 7 (1979). The entire disclosures of the patents and the Kirk-Othmer reference set forth in this paragraph are hereby incorporated by reference and relied upon.
An important improvement in clinical performance of polymer-based dental restoratives may be achieved and their scope of applications greatly expanded if their water sorption is lowered, mechanical strength and hardness improved and filler/resin ratio significantly raised. Accordingly, there is a need in the art to develop polymerizable compounds which tend to overcome the shortcomings of the prior art polymerizable compounds used in dental materials.